416 Scientific Intelligence. 
ployed was that of least deviation. According to Cauchy, the connection 
between the wave lengt and corresponding index of refraction is ex- 
pressed by the equation 
B 
< ae ’ 
in which A is the coefficient of refraction, and B the coefficient of > 
persion. If the indices ug and ty be determined by direct measuremen 
for a given substance, we have the two aon 
He =A+5 . 
a 
B 
by Pas 
7 
from which we find s 
—Uae 
B= aes Ps Swen Hy ne, 5 
Roa ph 7 
ee . 
ee 
Thus for water the indices found were . 
Mg == 133120 
Mg== 133723 ' 
From wu, and #y and the wave lengths 2 
4. — 6°533 ; a 
we obtain for the constants A and B at 19° C. the values 
A= 1:32386 
B = 0:31328, - 
Caleulating from these the value of wg, we find ug= 133722, = . 
agrees very closely with the actual rmonarreaniet 1°33723. For the < 
D the calculated index was 1-33290, the value found by direct measure — 
ment also 1°33290. The author gives the values o B for e ed 
substance at each temperature measured. With these values he also 
calculates the indices of refraction of each substance at th 
perature of 20° C. for the seven Fraunbofer’s lines ; = 
= 
> 
oe 
a 
formic and end with wnanthylie ane are as aio The edie of re 
fraction increase with the number of equivalents of carbon and hy er 
but by no means uniformly. The indices for all the increase “a 
about th as the wave lengths diminish. The curves 70 
same degr 
the different acids are not equidistant, but, excepting in the irvegt- 
formic acid, are nearly parallel. The coefficient A also Saag: °C. 
larly with the carbon and hydrogen. The diminution in A ne 
becomes Sa from acetic acid upward, but the differences are very | small. 
The ch in the case of formic acid is less than nin any of the 
cient B mente —— with the increase of carbon Phe ps 
the case nf fie acid. Also the elongation | 
